My first Express build...its alive!..pic added...question?

[guitarsnguns04]

my chassis has a shape that I beleive is the double d you are referring to. However I cant find a grommet to fit the existing hole. I do electrical work for a living and I dont even have anything at my office that would work. I could always punch it out and use a regular 3/8" round hole but I am now curious about what was originally used and what fits my chassis correctly.
Thanks for the input though it is appreciated.

[Noel Grassy]

sorry for the long winded explanation.
I hope someone will chime in about your bias pot question because I've wired mine like Francesca appears. With the 47K going to the wiper.

[Ron Worley]

Based on what I learned from the experienced guys here, that's not correct:

One side of the bias pot goes to the 47K (or 56K as suggested), the wiper goes to ground connected to the bias caps, and the other side of the pot to ground wired UNDER the board to the turret of the same bias cap that the wiper is connected to....

Perhaps Allyn or others will chime in here to comment on what is correct...

Ron

[guitarsnguns04]

Ron..thanks for chiming in. Mine is wired as you have explained it. I hope that is correct.

[Ron Worley]

GnG-

It's working beautifully, so I have to conclude that it's correct. I got this arrangement from very knowledgeable builders here, so I'm sticking with my setup....

Hey NG, watsa matter, you no believe me???

Ron

[guitarsnguns04]

Thanks Ron..I will proceed in that direction. As far as the build is going..I was doing great until I turned pin 1 on v4 to try to make it a little easier to connect to pin 8 and ground. You can probably guess the rest..I need a new socket. I am also short the 2 -1k/5w screen resistors...oops. I do have a question though. I substituted r15 with a 75k res. instead if a 82k. Is that a problem..or will I notice any difference at all or should I put in a 82k? I didnt have one at the time..backorder..and I thought I was going to finish it up before the arrived. Since I broke the terminal on the v4 socket. I have the 82k now I guess is it worth changing or am I being to cautious?

[Ron Worley]

GnG04-

I would change the resistor- the balance in the Phase Inverter is somewhat sensitive, so it might make the input to the power tubes a little off kilter..

I am no tube amp electronics expert, so the pros here will be better able to explain if I am right or not....

Ron

[guitarsnguns04]

Thanks for the reply Ron...anyone else want to chime in with their thought?

[UR12]

Thanks for the reply Ron...anyone else want to chime in with their thought?

There are a few ways to wire the bias pot and still have it function correctly. If you wired it like the original Kelly schematic, with the bias voltage coming off the wiper of the pot (like most older Marshalls), and the pot failed or the wiper became disconnected you would loose bias and cook your output tubes. The way Ken did Francesca and the way I run mine are pretty much the same in that you have the wiper also tied to one end of the trim pot. With it set up this way, in the event of a failure of the trimmer pot you would get max bias and your tubes would be safe. Both ways will work just fine but I always like to look at things and ask myself, What if?...............

[Ron Worley]

Dana- Thanks for explaining it... Now I remember that it was you who set me straight on the wiring of the bias pot to protect the tubes if the pot failed...

Ron

[guitarsnguns04]

Thanks ur12..what about the resistor change...75 vs 82?

[guitarsnguns04]

man...I am really close. I nedd a few parts still:
strain relief for the power cord..Allyns chassis
2-1k-5w screen resistors
1-octal socket..I broke pin 1 on accident.

everything else is ready to go...I have to find the screen res. and the strain relief and a replacement socket or 2..so they match. Anyone got these parts for sale to me asap?

[guitarsnguns04]

It looks like my parts shipped out yesterday...woo hoo! It shouldnt be long now and it should be making noise.

[guitarsnguns04]

HELP>>I have a lolin ck1455 rotary switch for my impedence selector. It is the one in Rons Bom. I am not sure how to set it up and wire it for my build. It has the lugs marked but I am not sure what goes to what. There are 2-#1 lugs which I verified with my meter and the one each of the rest of the 12 lugs.I read about a jumper wire needing to be installed etc. but I am lost..any help is appreciated for sure!

[guitarsnguns04]

a closer look at the actual pics ...there appears to be 4 jumper wires on the switch. White,red,yellow and black. I cant make out what terminals they are connecting to on the bottom side. I can see the solder on the lugs but am not sure what color goes to each lug on the bottom???? frustrating..lol The top connections are detailed in the pics quite well. Any help for a fellow builder? I would be greatful!